A cross-sectional study investigating the impact of dietary vitamin D intake and fortification in Jordanian adults with type 2 diabetes.

BACKGROUND: Vitamin D is crucial in maintaining bone strength and supporting immune function and may also influence metabolic health, including glycemic control. This study aimed to investigate the relationship between the vitamin D intake and markers of glycemic health in Jordanian adults with type 2 diabetes mellitus (T2DM). METHODS: This cross-sectional study was conducted on 240 patients with T2DM aged 42-69 years. Convenience sampling was used to recruit participants from hospitals across Jordan. Participants with conditions or medications impacting vitamin D status (e.g. celiac disease and antiepileptic drugs) were excluded from the study. Data on demographics, medical history, lifestyle, and dietary intake were collected using a structured questionnaire. Liquid chromatography with tandem mass spectrometry analysis was used to estimate the vitamin D content of commonly consumed foods. Serum 25(OH)D and glycated hemoglobin (HbA1c) levels were measured. Normality was tested using the Shapiro-Wilk test. Pearson's correlation and analysis of variance (ANOVA) were used to determine links between the dietary vitamin D intake, serum vitamin D levels, and glycemic outcomes. RESULTS: The mean dietary vitamin D intake was 150 ± 140 international units/day, with tuna, yogurt, pita bread, and non-fortified Ultra-High Temperature (UHT) milk as primary sources. Total dietary vitamin D intake showed no significant association with fasting blood glucose but was inversely correlated with HbA1c (r = -0.38, P < 0.05). Dairy (r = 0.42, P < 0.05) and fish (r = 0.35, P < 0.05) intakes were positively associated with serum 25(OH)D levels (mean: 21.3 ± 4.4 ng/mL), unlike meat, eggs, or bread. Higher income, education, and sun exposure were linked to higher levels of vitamin D in the serum. Vitamin D intake and status were found to be significantly associated with age, body mass index (BMI), frequency of breakfast consumption, and snack intake. CONCLUSION: Consuming vitamin D-rich sources, including dairy, fish, and fortified foods, was associated with higher serum vitamin D levels, which were related to better HbA1c levels. This suggests a potential benefit for glycemic control and broader diabetes management. A cross-sectional design makes it impossible to distinguish cause and effect, and factors such as supplement use or varying levels of food fortification complicate the interpretation of the results. Longer-term and intervention-based studies are necessary before a stronger claim can be made.